-LRB- CNN -RRB- -- Comprehensive immigration reform . Suddenly the phrase is on everyone 's lips . From President Barack Obama to rising Republican star Sen. Marco Rubio to right-wing television hosts Sean Hannity and Bill O'Reilly . As if by magic , everybody 's for it after six years of ducking and using reform as a political wedge issue -- everybody wants to get it done .

But what exactly is it ? What kinds of changes will it entail , and what will they mean for America ?

After more than 10 years of on-and-off debate in Washington , the most important piece of the puzzle is still rarely discussed and poorly understood . Obama often talks about reform without even mentioning it . It never came up on the campaign trail . It 's not what brought Latinos out to vote in record numbers . And although it 's likely to be included in the framework for reform expected to be released Monday by a bipartisan group of Senators , the concept gets very little attention from the media , English - or Spanish-language .

iReport : Under deportation , above fear

What 's the most important piece of comprehensive immigration reform you never heard of ? It 's fixing the legal system so it works for the future -- for immigrants and the U.S. economy .

Many Americans think reform is about the 11 million unauthorized immigrants already living in the United States . Many have been here for years and have put down roots . We 're not going to deport them -- not even the harshest restrictionists think that 's practical .

Nor are most likely to go `` home '' voluntarily , no matter how difficult we make their lives with tough enforcement . For the overwhelming majority , America is home by now . And they are sure to be the most contentious issue when the immigration debate resumes in months to come .

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But most contentious is not the same as most important .

We all must ask : What created this problem in the first place ? Exactly what is it about the broken immigration system that produced this vast underground world of workers and families -- a population the size of Ohio ?

The root cause : For less-skilled foreigners who want to come to work legally in the United States , there is no `` line '' -- no available visas .

The two existing programs for low-skilled temporary workers are for seasonal labor only : farmhands , landscaping crews , summer and winter resort workers . And there are virtually no permanent visas to be had for unskilled workers . There simply is no avenue for an uneducated Mexican unless he has family members living legally in the U.S. who can sponsor him for a family visa .

Many , if not most , of the 11 million already here would have preferred to enter the country legally if that were possible . But they and others like them have no lawful option .

This would n't be a problem if we did n't need immigrant workers . But we do . And we 're going to need them increasingly as the economy recovers .

This is n't because American workers are somehow lacking or inadequate . On the contrary , for the most part , it 's because Americans are doing better than in decades past . We 're becoming better educated and aspiring to the kinds of jobs for which our better educations prepare us .

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In 1960 , half of the native-born men in the labor force were high school dropouts happy to do physically demanding , low-skilled work . Today , less than 10 % of the native-born men in the labor force are high school dropouts . And meanwhile , far from shrinking , the demand for low-skilled labor is growing over time . In 1955 , for example , 25 cents of every dollar spent on food was spent in a restaurant . Today , the figure is nearly 50 cents . And one of the fastest-growing occupations in America is home health aide .

But very few Americans with high school diplomas aspire to careers as busboys or home health aides . And they should n't -- their educations equip them to do more productive work , making better wages and contributing more to the economy .

No , we do n't need as many immigrant workers in a down economy -- and far fewer want to come to the U.S. when jobs are scarce . But we still need some , and they need a legal way to get here . And whatever program we create needs to be flexible , growing in good times to accommodate rising labor needs and shrinking back in down times when demand subsides .

Do n't get me wrong : The goal of reform is not to increase the overall number of unskilled immigrants entering the country .

What 's needed is to end illegal immigration by creating ways for needed workers to come legally -- creating worker visas and establishing a system that allows employers who ca n't find enough willing and able Americans to connect easily and quickly with lawful immigrants .

This is not just an economic imperative . Without it , there can be no successful immigration law enforcement .

Even the best , most effective enforcement is no match for the dynamism of the U.S. economy . As long as there are jobs available , foreigners will want to come to work here . And if we want to prevent them from coming illegally , we need to create lawful alternatives .

Finding a solution for the 11 million unauthorized immigrants already in the country addresses the mistakes of the past but fixes nothing going forward . Unless we create ways for the immigrants of the future to enter legally , we 're going to find ourselves in exactly the same predicament a decade or two down the road -- wondering what to do about 10 or 20 million unauthorized immigrants living among us but beyond the rule of law .

The only way to prevent this : a legal immigration system that works .

Now if only Obama would mention it . Then we 'd have some hope of getting somewhere as the debate resumes .

The opinions expressed in this commentary are solely those of Tamar Jacoby

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Tamar Jacoby : Immigration reform in air , but focus tends to be on the undocumented

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She says for real reform , discussion must be on providing unskilled worker visas

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She says there 's no way to `` get in line '' if no visas are available

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Jacoby : In dynamic economy , entry will always outpace enforcement